Gases are employed in a wide variety of uses. Because of the very large volume difference between a fluid in its gaseous and liquid phases, the gas will often be stored at the use site in the liquid phase and vaporized into the gas phase as usage requirements dictate. This procedure is typically employed with cryogenic fluids which are in the gas phase at ambient conditions and are in the liquid phase at very low temperatures. Examples of such fluids include nitrogen, oxygen, argon, hydrogen and helium.
Such cryogenic fluids are stored at the use site in the liquid phase and vaporized to provide gaseous product for use. Typical examples include the vaporization of liquid oxygen for use at a medical facility and the vaporization of liquid nitrogen for use for blanketing or inerting purposes in a manufacturing process such as in the manufacture of integrated circuits or microchips. A typical installation includes a liquid storage tank and a vaporizer to vaporize the liquid. The vaporizer may be powered by any heat source such as electric heat, steam, hot water, and, in the case where the liquid is a cryogenic liquid, the heat in the ambient air. When an ambient air vaporizer is employed, a preferred such vaporizer is the wide space vaporizer disclosed and claimed in U.S. Pat. No. 4,399,660 Vogler, et al.
It is important that the vaporizer operate effectively because the delivery of non-vaporized fluid to the use point could be very harmful. Moreover, especially in the case of a cryogenic fluid, even if fully vaporized, the gas must be delivered to the use point at a sufficiently high temperature to avoid damage. This temperature is generally at least about -40.degree. F.
The liquid storage tank-vaporizer assembly is expected to operate unattended, 24 hours a day, under all weather conditions. Thus, it is important that any temperature sensitive control valve that may be employed to guard against unacceptably low fluid temperature flow be resistant to exogenous set point upsets such as sudden and severe changes in ambient conditions.
Accordingly, it is an object of this invention to provide a pilot valve for affording low temperature protection in fluid flow while providing system integrity for protection against ambient upsets.